- "Dustin once posted an explanation on antenna diversity that explains this quite well. This is a snippet of that document (From Cisco). "A diversity antenna system can be compared to a switch that selects one antenna or another, never both at the same time. The radio in receive mode will continually switch between antennas listening for a valid radio packet. After the beginning sync of a valid packet is heard, the radio will evaluate the sync signal of the packet, on one antenna, then switch to the other antenna and evaluate. Then the radio will select the best antenna, and use only that antenna for the remaining portion of that packet. "On transmit, the radio will select the same antenna it used the last time it communicated to that given radio. If a packet fails, it will switch to the other antenna and retry the packet.
"One caution with diversity, it is not designed for using two antennas, covering two different coverage cells. The problem in using it this way, is that if antenna #1 is communicating to device #1, while device #2 (which is in the antenna #2 cell) tries to communicate, antenna #2 is not connected (due to the position of the switch), and the communication fails. Diversity antennas should cover the same area, from only a slightly different location." -- JacobFarkas
And JimThompson writes "The AP doesn't always get to control the antenna switches. Some designs just leave the switch set to where it was during the last reception.